The invention relates to a process for producing a carbon film on a substrate.
Carbon films are used in many technical areas for the most varied of tasks, for example, as a coating to provide protection against high energy radiation, as a conductive coating or for the purpose of achieving a high emission capability for radiant cooling. The "sputter" technique (cathode sputtering) is a frequently used method for producing carbon films, whereby in a vacuum-gas discharge particles of cathode materials which are released from the cathode surface by impacting ions of the gas discharge deposit themselves on an adjacent substrate where they form a layer, the nature of which is determined by virtue of the conditions with respect to the gas composition, the gas pressure, etc. It is known for the purpose of depositing carbon by means of the sputter technique to use a gas atmosphere with argon or another inert gas. Sputtering of carbon and carbon-nitrogen layers using a high frequency sputter technique is described for example by Y.-A. Li et al., Journal of Materials Science Letters, Vol. 17(1998), Pages 31-38.
A known problem when sputter-depositing carbon, for example, in an argon atmosphere, is that they layers produced in this manner experience an extremely high level of compressive strain, the value of which can be in excess of 100 MPa up to in the region of some GPa, as described, for example, by E. Broitman et al., Applied Physics Letters, Vol. 72, No. 20 (1998), Page 2532. In most cases, the compressive strains lead to the formation of folds and waves on the surfaces on which the carbon layers have been deposited and this renders the layer unusable as well as impairing the adherence to the substrate and/or can adversely affect or even destroy the substrate surface or the entire substrate itself.
A further disadvantage of known carbon layers produced by sputtering is the lack of resistance of the layers to moisture and other contaminants when stored in air.